Explain the historical significance of the Compromise of 1850, the Kansas Nebraska Act, and the secession of the South in particular.

The Compromise of 1850 and the Kansas Nebraska Act of 1854 were attempts to compromise on slavery during the period when the United States was expanding westward. However, the trend towards compromise was ultimately futile, as the Civil War broke out in 1861.
The Compromise of 1850 was an attempt to resolve the disputes that arose as a result of the Mexican-American War of 1846 to 1848. The compromise made California a free state (one that did not have slavery), while the Utah and New Mexico Territories were allowed to practice popular sovereignty, meaning that they could decide whether or not they wanted to permit slavery. The slave trade (but not slavery) was abolished in Washington, D.C., but there was a more forceful fugitive slave law that greatly angered abolitionists.
The Kansas Nebraska Act allowed people in those territories to decide whether or not they wanted to permit slavery. It effectively repealed the Missouri Compromise, which had disallowed slavery north of the 36-30 line of latitude. As a result of this act, pro-slavery and abolitionist forces clashed in the years before the Civil War, giving rise to the term "Bleeding Kansas." These compromises were ultimately ineffective because both sides of the slavery debate had become too heated to rely on compromises, and the South seceded after the election of Abraham Lincoln in 1860 (he assumed office in 1861).